Vibration-measure.



A. F. Z AHM.

VIBRATION MEASURE.

APPLICATION men NOV. n. 1915.

1,3 1 6,260. I Patented Sept. 16, 1919.

'IIII/I/IIIIA I avweuto'c 1 ALBERT F. ZAHM.

1 UNITED STATES PATENT ALBERT 1". ZAHM,

or BUFFALO, NEW roux, Assmnon-To cun'rlss mama m MOTOR CORPORATION, A CORPORATION OF NEW YORK.

VIBRATION-MEASURE.

Buffalo, in the. county of Erie and State of New York, have invented certain new and useful Improvements in Vibration-Measures, of which the following is a specification.

My invention relates to that class of vibration measures designed particularly for demay be so modified without departing in any wi'se'from the generic spirit of the invention as to adapt it for use in measuring the natural periods of vibration of bodies of similar character. Aerial propellers are at this time generally made of wood. The Wood is highl seasoned, the structurelammated and the b ades themselves are subject to .a variable pressure of the air rush in which the propeller operates and by means of which it derives its thrust. This variable pressure places the blade under considerable tension. At the same time the blade'is subjected a vibration due to the vibration, at various speeds of revolution, of the driving motor. It not infrequently happens that at some speed of the motorthe imposed vlbrations are in harmony with the natural period of the propeller itself withthe r'esu lt that the blade, already flexed under its driving load,

is placed immediately in its fundamental vibration, the amplitude of'which is soon driven to itsmechanism by opening the approach to or actually reaching out tothe state of resonance between the motor vibration and the propeller vibration. Under these conditions there are set up in the blade complex strains ofa very severe character which have been known in a number of instances to crack the propeller'blade and in numerous others to split it wide open. The moment the pressures and weights are un- "equalized, centrifugal action and the unbalanced condition result in entire destruction. The sequence of causes and efi'ects is probably not the same in all instances but in 'eneral it may be said that the blade is initially cracked or split due either to the vibration or the unequal distribution of pressures incitermining the natural period of vibration of.

Specification of Letters Patent. Pafelitdspil. 16, 1919, Application fil ed November 17, 1916. Serial Illo. 181,959.

dent to vibration whereupon the pressures are still further distributed and in turn so distort the blade that centrifugal forces accompaniedby continued violent vibration completes the wreck. I v

By determining the natural'period of the propeller in advance and regulating .this natural period .so that it. differs from .the period of motor vibration within the usual motor speed ranges, allv of these difiiculties can be effectually eliminated. The determination of this natural period and its adjustment is 'efi'ected th'roughthe use'of the instrument of m invention.

Broadly speaking, my invention comprises a rigid base member elongated in form and of such mass and rigidity that its period of vibration is far removed from the riod of vibration 'of the propeller un er test. Clamping means are associated with this base and adapted to clampthe propeller at its hub to the base with a, rigidity a proximating. that with which the prope er itself is clamped to the driving shaft of the motor. Also mounted on the same base and removed from the clamping means is an elevated structure adjustable to and from the clamping means aforesaid so as to accommodate propellers of'various diameters. Supported from this structure is a timing and recordin element in the specific embodiment disclose orced thereto so that there is traced thereon the record of vibration in the course of the travel of the timing element'past the tip of the'vibratin blade.

Figure 1 1s a side elevation of the vibration measuring machine showing the relation of the propeller to the measuring elements; r

Fig. 2 is a perspective view on an enlarged scale; Y V

Fig. 3 is a perspective diagrammatic view illustrating the operation;

Fig. l is a section showing the waxed plate upon which the record is made Fig. 5 is a face view of the plate after record has been traced.

Fig. 6 is a modified form of pendulum an support.

In Fig. 1, C is a base constructed of sufficient mass and rigidity that it is not subject to any of the vibrations which may come to it through the vibration of the other elements of the machine. To this base C is rigidly fastened the pedestal S which sup orts the propeller by its hub B. At the en of the base C is a frame D which may be adjusted alon C for propellers of various lengths. At tie upper part of the frame D is a bolt H Which forms the pivotal point 0 from the pendulum E. At the lower end of the pendulum E is a waxed plate A Which is attached thereto ,by means of a suitable socket K. The pendulum is So arranged at the pivotal point 0 that it may be varied in length to bring the parts into proper relationship. F is a pointer which is securely fastened to the tip of the propeller by embedding in the Wood thereof or by other suitable means; so that the pointer has no vibration period of. its own but partakes of that of the propeller.

The operation of the vibration measuring machine is as follows. The propeller P is securely clamped by its hub B to the pedestal S by a suitable clamping device such as trunnion T and. nut N (Fig. 1) and in such a position that the axis of the blades is perpendicular to the waxed plate A. The plate A is waxed over its surface and smoothed off to present a perfectly plane surface on which the record is to be traced and fastened in the socket. K. This waxed surface is conveniently formed by pouring on a perfectly plain table such as that formed by a piece of plate glass and thereafter attached to plate A by sticking upon pins a, projecting from the face of'the plate itself. The frame D is so adjusted along C that the waxed ri l ate A makes contact with the pointer F. endulum E is swung to a known position X (Fig. 3) through an angle (1 degrees from the vertical line through 0 and F where it is held by hand or suitable stops. Vibrations are set up in the propeller blade by striking at a point G which has been so determined that fundamental vibrations are induced by the blow.

The propeller having been set into vibration the pendulum is released and in describing the are XZY the pointer F traces a curve or record of vibration upon the waxed surface A. The pendulum is stopped at the point Y in order that the record may not become marred due to the decreasing amplitude of the propeller vibrations and to possible asynchronism of the superposed record,

The time required for the surface to pass the pointer may be computed from the law of the pendulum which gives the time of a single oscillation as represented by th l ti wherein tis time in seconds. I is pendulum length in centimeters and g is the value of the acceleration of gravity. The relationship is true only when the amplitude of vibration of the pendulum is comparatively small. The length of are through which the pendulum swings is calculated from the angle a be fore mentioned.

The above data is sufiicient for computing the time required for the pendulum E to .pass the pointer F.

The number of vibrations of the propeller represented by the curve traced upon the surface A are counted, hence from this data the vibration period of the propeller is computed.

In case it is desired to obtain the vibration period of the propeller taken in conjunction with the motor, engine beds, etc., the pendulum and support as shown in Fig. (3 are used. The propeller is mounted directly upon the motor crankshaft extremity in its operating position, and placed preferably in a horizontal position. The pendulum support of Fig. 6 is then rigidly mounted in suchposition that its Waxed record surface can contact with the pointer carried by the vibrating propeller tip. The modified form of pendulum is necessary by reason ofthe fact that the propeller is vibrating in a horizontal plane when mounted in this po sition.

WVhat I claim is:

1. An apparatus for measuring the vibration of heavy bodies comprising a rigid base of considerable mass having a period of vibration removed from that of the member whose vibration rate is to be determined, a clamping device rigidly connected with said base and adapted to clamp the member thereto, a timing-device also supported from said base in cooperative relation with said mem- 110 her, and arranged to travel in a plane at right angles to a radius line passing through said clamp and a recording means carried by one of said cooperative members.

2. An apparatus for measuring the natu- 115 ral period of vibration of propellers, comprising a rigid base of considerable mass .aving a rate of vibration removed from that of the propeller whose vibration is to be measured, a pedestal rigidly secured to 120 said base and having clamping connections for securing the propeller to the base, the rigidity of which approximates that of the driving shaft connections through which the propeller is arranged to be driven when in 125 use, and'a timing element rigidly mounted with respect to said base and arranged to travel in a plane at right angles to the ra-.

vibrations thereof.

3. An apparatus for measuring the natural period of vibration of propellers, comprising a rigid base of considerable mass having a rate of vibration removed from that of the propeller whose vibration is'tobe measured, a pedestal rigidly secured to said base and having clamping connectionsfor securing the propeller to the base, the rigidity of which approximates that of the driving shaft connections through which the propeller is arranged to be driven when in use,

. a vibration measuring means mounted rigidly with respect to said base and arranged in juxtaposition'to said blade, said means comprising a pendulum adapted to swing past said blade, whereby the rate of vibration of the blade is indicated thereon.

4. An instrument apparatus for measuring the natural period of vibration of propellers, comprising a rigid base, clamping means rigidly connected withsaid base and arranged toclamp the propellerto be tested rigidly thereto, together with a vibration measuring apparatus, adjustable readily to-.

Ward and from said clamping device whereby propellers of different diameters may be readily accommodated.

5. In an apparatus for measuring the natural period of vibration of propellers, in

combination, a rigidbase,-a clampin device for propellers rigidly connected t erewith, together with a vibration measure having an element arranged to coo erate with the vibrating tip of the propel er and adjustable vertically of said base whereby it may cooperate with portions of propellers located at different elevations, one of said cooperating members carrying a recording surface.

6. In an apparatus for measuring the natural period of vibration of a body, the combination of a support for the body whose vibrations are to be measured with a penduluin adapted to swing inthe path of a recording instrument carried by the body, said pendulum carrying a recording surface which is operated upon by said vibration recording instrument, whereby the natural period of the body may be determined from the record made and the natural law of the pendulum.

7. In an apparatus for, measuring the 1 vibrating recording instrument, whereby the natural period maybe determined from the record made and the natural law of the pendulum..

In testimony whereof I alfix my signature.

. ALBERT, F. ZAHM;

I ing surface which is operated upon by said 

